Mule deer and Rocky Mountain elk develop chronic wasting disease that belongs to the group of transmissible spongiform encephalopathies (TSEs). The PrP gene coding region has been analyzed in mule deer and Rocky Mountain elk. The predicted amino acid sequence of PrP was nearly identical (99.6%) between two species, with only a single difference at codon 226 (glutamine and glutamic acid, respectively). A polymorphism at codon 138 (serine to asparagine) has been detected in mule deer PrP gene coding region. Further investigation is underway to establish if this polymorphism plays a role in susceptibility of mule deer to chronic wasting disease. Analysis of 300 transmissions of different forms of TSEs to nonhuman primates revealed that rhesus monkeys had the lowest rate of successful transmission. Analysis of the PRNP gene has been initiated to elucidate the role of genetic factors in susceptibility of rhesus monkeys to TSE.